Enlarge ImageRequest to buy this photoMario Aguilera | Scripps Institution of Oceanography,A study found there’s less trash floating on the oceans than experts expected. Here, garbage mars the Pacific in 2009.

NEW YORK — Plastic junk is floating widely on the world’s oceans, but there’s less of it than
expected, a study says.

Such ocean pollution has drawn attention in recent years because of its potential harm to fish
and other wildlife.

The new work drew on results from an around-the-world cruise by a research ship that towed a
mesh net at 141 sites, as well as other studies. Researchers estimated the total amount of floating
plastic debris in open ocean at 7,000 to 35,000 tons.

Andres Cozar of the University of Cadiz in Spain, an author of the study, said that’s a lot less
than the 1 million tons he had extrapolated from data reaching back to the 1970s.

The new estimate includes only floating debris, not plastic that might be beneath the surface or
on the ocean floor.

Of the plastic pieces caught by the ship’s net, most were less than about one-fifth of an inch
long. Some floating pieces start out small, such as the micro-beads found in some toothpastes and
cosmetics or industrial pellets used to make plastic products. Other small pieces can result when
wave action breaks up larger objects, such as bottle caps, detergent bottles and shopping bags.

The net turned up fewer small pieces than expected, and it will be important to figure out why,
researchers said. Perhaps the tiniest pieces are being eaten by small fish, with uncertain effects
on their health, Cozar said in an email.

While the research showed plastic to be distributed widely, concentrations were highest in five
areas that were predicted by ocean current patterns. They are west of the United States, between
the United States and Africa, west of southern South America and east and west of the southern tip
of Africa.

Plastic debris from land reaches the ocean mostly through storm-water runoff, the researchers
said in their report, released last week by the
Proceedings of the National Academy of Sciences.

Kara Lavender Law, who studies plastic pollution at the Sea Education Association in Woods Hole,
Mass., said the study provides the first global estimate she knows of for floating plastic
debris.

The estimate appears to be in the ballpark, given the results of prior regional studies, said
Law, who didn’t participate in the new work.

“We are putting, certainly by any estimate, a large amount of a synthetic material into a
natural environment,” Law said. “We’re fundamentally changing the composition of the ocean.”

The impact on fish and birds is hard to gauge because scientists don’t understand things like
how much plastic animals encounter and how they might be harmed if they swallow it, she said.